Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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QUADRILATERAL ASSEMBLY FOR COHERENT JET LANCING
AND POST COMBUSTION, IN AN ELECTRIC ARC FURNACE
Technical Field
This invention relates generally to electric arc
furnace practice and, more particularly, to coherent
jet practice in an electric arc furnace.
BackcLround Art
A recent significant advancement in the field of
gas dynamics is the development of coherent jet
technology which produces a laser-like jet of gas which
can travel a long distance while still retaining
substantially all of its initial velocity and with very
little increase to its jet diameter. One very
important commercial use of coherent jet technology is
in electric arc furnace practice such as for providing
gas for lancing. Any improvement in coherent jet
practice in conjunction with electric arc furnace
operation would be very desirable.
Accordingly it is an object of this invention to
provide a system wherein coherent jet practice and
other operations of an electric arc furnace may be
carried out with greater effectiveness.
Summary Of The Invention
The above and other objects, which will become
apparent to those skilled in the art upon a reading of
this disclosure, are attained by the present invention,
one aspect of which is:
A quadrilateral assembly suitable for installation
into a wall of an electric arc furnace comprising a
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coherent jet opening for providing a coherent jet of
gas at a first downward angle into the electric arc
furnace, a carbon injection nozzle below and/or to the
side of the coherent jet opening, and at least one post
combustion nozzle for providing at least one oxidant
stream into the electric arc furnace, said oxidant
streams) being at a second downward angle which is
shallower than said first downward angle.
Another aspect of the invention is:
A quadrilateral assembly suitable for installation
into a wall of an electric arc furnace comprising a
coherent jet opening for providing a coherent jet of
gas at a downward angle into the electric arc furnace,
a carbon injection nozzle below and/or to the side of
the coherent jet opening, and a plurality of post
combustion nozzles for providing a plurality of oxidant
streams into the electric arc furnace, said post
combustion nozzles oriented such that the oxidant
streams converge to form a sheet of gas within the
electric arc furnace.
A further aspect of the invention is:
A method for providing gas into an electric arc
furnace comprising passing a coherent jet of gas from a
coherent jet opening of a quadrilateral assembly
downwardly into the electric arc furnace at a first
downward angle, passing a first stream of post
combustion oxidant from a first post combustion nozzle
of the quadrilateral assembly into the electric arc
furnace at a second downward angle which is shallower
than said first downward angle, passing a second stream
of post combustion oxidant from a second post
combustion nozzle of the quadrilateral assembly into
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the electric arc furnace at an angle so as to converge
with the first stream of post combustion oxidant, and
forming a sheet of post combustion oxidant from said
first and second streams of post combustion oxidant
within the electric arc furnace.
As used herein, the term "coherent jet" means a
stream of gas whose diameter remains substantially
constant along its length. A coherent jet is typically
surrounded by, i.e. is within, a flame envelope, and
typically has a supersonic velocity.
As used herein, the term "lancing" means providing
gas from a gas stream above the surface of a liquid
into the liquid.
As used herein, the term "post combustion" means
providing oxidant into an electric arc furnace for
combustion with combustible matter above the surface of
molten metal within the surface.
Brief Description Of The Drawings
Figure 1 is a cross sectional representation of
the operation of an electric arc furnace.
Figure 2 is a head on view of one preferred
embodiment of the quadrilateral panel or assembly of
this invention.
Figure 3 is a simplified side view illustrating
the post combustion oxidant sheet embodiment aspect of
this invention.
Figure 4 is a head on view of one preferred
embodiment of the quadrilateral panel or assembly of
this invention using oxidant sheet post combustion
practice.
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Detailed Description
The invention will be described in detail with
reference to the Drawings. Referring now to Figure 1,
there is shown electric arc furnace 20 having sidewall
21 and bottom wall 22 and containing a bath comprising
a pool of molten metal 23. Generally the metal will
comprise iron or steel. Slag layer 24, which may be
molten or solid is also illustrated above the pool of
molten metal, and scrap metal layer 25 is shown above
slag layer 24. The slag layer generally comprises one
or more of calcium oxide, silicon dioxide, magnesium
oxide, aluminum dioxide and iron oxide. The scrap
layer, if present, is melted by heat provided by
electrodes 26 to form molten metal pool 23. The molten
metal pool comprises, in addition to metal, oxidizeable
matter such as carbon and/or hydrocarbons. Exhaust is
passed out of the furnace using exhaust conduit 27.
Gas is passed into the furnace from the sidewall
for lancing or for combustion to assist in scrap
melting and/or maintaining a sufficient temperature to
ensure molten conditions. Gas may also be passed into
the furnace for post combustion. Moreover,
carbonaceous material may be passed into the furnace
for mixture with the molten metal for combustion with
lanced oxygen. Heretofore such operations have been
carried out separately, i.e. using separate assemblies,
and/or using imperfectly fitting cylindrical conduits
in the walls of the furnace. The invention provides
significant advantages over conventional practice.
In the practice of this invention, lancing gas,
post combustion oxidant and carbonaceous material are
all provided into the electric arc furnace using a
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quadrilateral assembly. Preferably the quadrilateral
assembly has 90 degree included angles. One or more
such quadrilateral assemblies may be used with a
furnace.
Referring now to Figure 2, quadrilateral assembly
40 comprises first quadrilateral portion 1, which in
this embodiment is a square, and second quadrilateral
portion 2, which in this embodiment is a rectangle.
Quadrilateral assembly 40 is suitable for installation
into a sidewall, preferably flush with the sidewall, of
an electric arc furnace, positioned so as to provide
gas into the furnace as illustrated in Figure 1. The
assembly is typically water cooled and typically about
four inches thick. Typical dimensions for portion 1
are 12x12 inches and for portion 2 are 6x12 inches
although any other suitable dimensions may be used.
Portion 2 may be on the left, on the right or above
portion 1.
Coherent jet opening 3 is positioned in portion 1
of quadrilateral assemb1y,40. Typically assembly 40 is
located in the wall 21 of the furnace such that
coherent jet opening 3 is from 24 to 50 inches above
the surface of the molten metal. Coherent jet opening
3 houses a coherent jet injector which provides a
coherent jet 41 into the furnace at a first downward
angle toward the molten metal. The first downward
angle is typically within the range of from 35 to 50
degrees to the horizontal, preferably about 40 degrees.
Coherent jet 41 may be injected straight into the
furnace relative to the sides of quadrilateral assembly
as shown in Figure 2, or may be angled sideways to
the left or right. If angled sideways, the sideways
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angle should not exceed 30 degrees and preferably
should not exceed 20 degrees. U.S. Patents 5,814,125
and 6,096,261, for example, may be referred to for
information describing methods and structures for
generating coherent jets. Typically the coherent jet
injector will comprise a converging/diverging nozzle
and a flame envelope provision means in a ring around
the converging/diverging nozzle. Any gas may be used
as the gas for making up the coherent jet. Examples
for such gases include pure oxygen or oxygen-enriched
air, which are particularly useful when the gas is used
for combustion in the electric arc furnace, and an
inert gas, such as argon, or mixtures of one or more
inert gases, which are particularly useful when the gas
is used for stirring in the electric arc furnace.
Below and/or to the side, preferably below and to
the side, of coherent jet opening 3 of quadrilateral
assembly 40 is carbon injector nozzle 4 which is used
to provide a stream 42 of carbonaceous material into
the furnace. The carbonaceous material is typical
powdered coal in a carrier gas, but may also be liquid,
e.g. oil, or even gaseous, e.g. methane, propane, etc.
The carbonaceous material stream 42 is directed toward
the molten metal and is preferably oriented at an angle
such that the carbonaceous stream 42 and the coherent
jet 41 impinge on the molten metal bath at about the
same point. In the case where the coherent jet is
angled sideways, the carbon injector nozzle preferably
is on the side where the jet is angled so as to
minimize the length the carbonaceous stream has to
travel before meeting the coherent jet at the bath.
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The quadrilateral assembly also includes at least
one post combustion nozzle. In the embodiment
illustrated in Figure 2, post combustion nozzles 5, 6
and 7 for providing post combustion oxidant into the
furnace are located in quadrilateral assembly 40. In
the embodiment illustrated in Figure 2 the plurality of
post combustion nozzles 5, 6 and 7 are located in
quadrilateral portion 2 of quadrilateral assembly 40.
Each post combustion nozzle provides a stream 45, 46
and 47 respectively of oxidant for post combustion
within the furnace. The oxidant may be air, oxygen-
enriched air or pure oxygen. Generally the post
combustion oxidant has an oxygen concentration of at
least 70 mole percent, preferably at least 90 mole
percent, most preferably at least 95 mole percent. The
post combustion oxidant stream or streams have a
generally subsonic velocity, generally within the range
of from 100 to 980 feet per second and typically within
the range of from 0.20 to 0.75 Mach.
Figure 2 illustrates one preferred embodiment
wherein the plurality of post combustion oxidant
streams are each passed into the furnace at a second
downward angle which is shallower than the first
downward angle and is generally within the range of
from 20 to 30 degrees to the horizontal. The post
combustion oxidant streams could all be at the same
downward or sideway angles although generally they are
at different downward angles so as to better cover the
area of the molten metal where carbon monoxide
evolution occurs.
Figure 3 illustrates another preferred embodiment
of the invention wherein at least two post combustion
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oxidant streams converge to form a post combustion
oxidant sheet. Referring now to Figure 3, first post
combustion oxidant stream 50 is injected into the
furnace from first post combustion nozzle 51 and second
post combustion oxidant stream 52 is injected into the
furnace from a second post combustion nozzle 53. The
two post combustion nozzles are generally from 3 to 8
inches apart, typically about 4 inches apart, as shown
by L in Figure 3, and inject their respective post
combustion oxidant streams at an angle toward each
other so that they form an angle theta when the post
combustion oxidant streams converge. Theta is
generally within the range of from 5 to 45 degrees,
preferably within the range of from 10 to 20 degrees,
and typically about 12 degrees. The converging post
combustion oxidant streams form a post combustion
oxidant sheet 54 which serves to improve the contact of
the oxygen of the post combustion oxidant with
oxidizable species in the headspace of the electric arc
furnace thereby improving the efficacy of the post
combustion. The convergence of the post combustion
oxidant streams to form the sheet serves to limit the
penetration of each post combustion oxidant into the
furnace while still retaining a high velocity for the
post combustion oxidant streams.
Figure 4 illustrates the operation of the
invention using the post combustion oxidant sheet. The
numerals of Figure 4 are the same as those of Figures 2
and 3 for the common elements and these common elements
will not be described again in detail. Generally the
downward angle of the post combustion oxidant sheet
will be within the range of from 10 to 40 degrees from
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the horizontal, preferably within the range of from 20
to 30 degrees, and typically about 25 degrees.
Although the invention has been described in
detail with reference to certain preferred embodiments,
those skilled in the art will recognize that there are
other embodiments of the invention within the spirit
and the scope of the claims.
